Seasonal changes of the adrenocortical responses to stress in redpolls, Acanthis flammea, in Alaska

Male and female redpolls Acanthis flammea showed marked increases in circulating corticosterone up to 1 hour after exposure to a common stress—capture, handling and restraint—indicating that their hypothalamo‐pituitary‐adrenal axis responded to acute stress in a manner similar to that of other vertebrates. We used this protocol as a measure of responsiveness of the adrenocortical cells to acute stress in general and for comparison with gender and across seasons. In both sexes the adrenocortical response to stress was reduced in January (at Fairbanks, 64°N) and maximal when birds were breeding in June at Toolik Lake (69°N). The elevation of circulating corticosterone following capture and handling in breeding males at Barrow (71°N) was significantly less than in breeding males at Toolik Lake. There were also considerable variations among individuals in the intensity of the adrenocortical responses, particularly in the maximum levels of corticosterone attained. This individual variation correlated significantly with fat score and/or body mass in both sexes only in breeding birds at Barrow. This difference may be explained by generally lower, and thus reduced variability in body fat and mass in birds sampled in the warmer climate of Toolik Lake. A similar trend was seen in non‐breeding birds, but this was not significant. Additionally, in January, baseline cortisterone levels in males were correlated with body mass, although this relationship did not hold when both sexes were considered. Body mass and fat score in winter were similar to those of redpolls sampled at Barrow in June. These data suggest that redpolls may be able to adjust their responsiveness to acute stresses in relation to fat stores. Those with greater fat depots had reduced responsiveness to stress. © Wiley‐Liss, Inc.